LIPID-METABOLISM IN LEAVES FROM YOUNG WHEAT (TRITICUM-AESTIVUM CV HEREWARD) PLANTS GROWN AT 2 CARBON-DIOXIDE LEVELS

Lipid synthesis was studied in primary leaves from 7-d-old wheat plant s which had been grown at either ambient CO2 concentration (350 mu mol mol(-1)) or elevated CO2 (650 mu mol mol(-1)) by incubating tissue sa mples with [1-C-14]acetate, Growth at different CO2 concentrations did not affect the total incorporation of radiolabel into lipids but it d id influence the relative labelling of individual lipid classes, such as diacylglycerol. The leaf basal segment was also studied separately and growth in an enriched CO2 atmosphere was associated with a dramati c increase (over 6-fold) in diphosphatidylglycerol (cardiolipin) label ling, indicating an increased rate of mitochondrial membrane biogenesi s, Immunocytological observations correlated with this metabolic resul t. Both leaf samples showed significant decreases in pigment and surfa ce wax labelling caused by growth at elevated CO2. Growth at different CO2 concentrations also influenced fatty acid labelling patterns, par ticularly those of the major labelled membrane lipids of the primary l eaf whereby there were changes in their ratios of radiolabelled 16 car bon to 18 carbon fatty acids. Phosphatidylglycerol was characterized, for instance, by increased palmitate labelling after wheat was grown i n elevated CO2 concentrations, In contrast, phosphatidylcholine was ma rked by a dramatic decrease in palmitate labelling but a corresponding increase in labelling of its 18 carbon unsaturated fatty acids, The d iacylglycerol fraction showed increased unsaturation of its C18 fatty acids. In addition, changes to the fatty acid moieties from the basal segment lipids were also associated with changes in the amount of labe lling of the polyenoic fatty acids of monogalactosyldiacylglycerol. Po ssible reasons for these changes in lipid labelling are discussed. The data show that growth in elevated atmospheric CO2 concentrations caus es significant changes in the metabolism of leaf lipids as well as inc reasing mitochondrial biogenesis.